Environmental considerations have lead to a comprehensive research with the aim of developing new technologies which may replace gasoline as the primary fuel for powering vehicles and vessels of different kinds. Pollutants produced by today's transport means include carbon monoxide and carbon dioxide, nitrogen oxides and sulphur oxides, hydrocarbons and particulates, and increasingly stricter rules and regulations in order to reduce or eliminate pollutants of this kind have for instance forced the car producers to consider the use of cleaner fuels or alternative methods for powering the vehicles. Hydrogen is the ultimate clean fuel, as the only combustion product is water. Hydrogen may with minor modifications be used in a conventional internal combustion engine. Hydrogen may also be used in a fuel cell powering vehicles and this seems in fact to be the best solution currently available. Another currently used technology is vehicles powered by electrical batteries. Both hydrogen-powered and battery-powered vehicles have zero pollutant emission.
A major obstacle which has prevented hydrogen from being the primary choice as clean fuel for use in vehicles, is the problem of storing hydrogen in the vehicles. Extensive research activity has in the past 30 years been centered on storing hydrogen in the form of solid metal hydrides. Metal hydrides are generated exothermally when metals and alloys are exposed to hydrogen. The hydrogen decomposes to atomic hydrogen in an exothermal reaction and subsequently enters interstices in the metal lattice. The hydrogen is recovered for use by heating, which in the present context may take place by means of the heat of combustion. The advantage of using metal hydrides for hydrogen storage is based on the fact that their volume density is very large. In reality the volume density of many hydrides is larger than that of solid hydrogen, for instance there are 4.3.times.10.sup.22 H atoms/cm.sup.3 in solid hydrogen at 4.2 K while there are almost twice as many in TiH.sub.2, i.e. 9.2.times.10.sup.22 H atoms/cm.sup.3. The major disadvantage is among others caused by low values for the hydrogen content based on weight or unacceptable high temperatures for the hydrogen recovery. The well-known hydrogen storage systems FeTiH.sub.2 and LaN.sub.2 and LaNi.sub.5 H.sub.6 contains for instance 1.9 and 1.5% by weight hydrogen and even though they have acceptable recovery temperatures, their hydrogen content is too low for use in vehicles. MgH.sub.2 and TiH.sub.2 have in contrast thereto higher hydrogen content, respectively 7.6 and 4.0% by weight, but must be heated to high temperatures in order to recover the hydrogen. Disproportionation, poisoning and accompanying loss of capacity and the need for regeneration of some of the storage alloys are also serious drawbacks.
Onboard storage of hydrogen in the form of gas or liquid is also a possibility. Compressed hydrogen is a relatively inexpensive alternative in onboard storage, However, weight and volume considerations make this alternative little attractive. Even if liquid hydrogen is acceptable with regard to weight and volume, it is very expensive due to the need for cooling the gas to 21 K and maintaining a low temperature in order to prevent hydrogen loss due to evaporation. Safety requirements also appear as potential drawbacks.
Hydrogen adsorption on activated carbon is another possible method for hydrogen storage. Hydrogen is in this case physisorbed at low temperatures on an active carbon material with high surface area. An advantage of this method is that only low energy is required to recover the hydrogen. However, the method requires the system all the time to be maintained at a low temperature in order to prevent a build up of the hydrogen gas pressure to dangerously high levels.
U.S. Pat. No. 5,614,460 (Schwartz & al.) discloses a method for producing microporous carbon materials which may be used as storage media for light fuel gases such as methane or hydrogen or as catalyst supports. U.S. Pat. No. 5,653,951 (Rodriguez & al.) generally concerns storage of hydrogen in layered nanostructures in form of carbon nanotubes, carbon nanofibrils, carbon nanoshells and carbon nanofibres. Hydrogen is chemisorbed in the interstices in the nanostructures. The method for storing hydrogen according to this patent specification discloses the use of nanostructures with a surface area of 50 800 m.sup.2 /g, a crystallinity of at least 50% and interstices in the crystalline areas with a size from 0.335 to 0.67 nanometers, the surfaces in the nanostructures defining the interstices being stated as having to posses chemisorption properties with regard to hydrogen. The method comprises introduction of hydrogen in a vessel at a pressure of at least 300 torr. However, the production of the stated materials in large volumes is difficult and reproducible absorption results have also turned out to be difficult to achieve.